Expert: Jeff Grigg - 1/13/2008

Question
Hi Jeff, This is a 2 part question, Please see if you can help. (A) I have just bought a 4M  g/f boat with a 1971/2 mercury 500 thunderbolt manual pull start motor on it serial no 3009972, it is a 4 cylinder 2 stroke motor.
When accelerating from the neutral position at about 30% the motor goes in to gear and thereafter very little acceleration until almost the fully forward position and if forced further it then accelerates, at this position the right hand side start accelerator leaver is also pulled/forced forward by the accelerating action. It's as if: (1) the carb is not opening fully. (2) The accelerator linkages are incorrectly adjusted. I cannot find a place on the carbs to manually open the carbs in the neutral idling position with my finger or a screwdriver to check whether the linkage and the carb are fully open at the same time. Please describe this and provide a means to check this, and also describe how to remove the linkages to adjust them.
(2) Can a starter motor be fitted? Will I need a new upper part of the motor with ring gear etc? what are the part numbers?
I hope you will be able to help and lastly I have no workshop manual.
Thanks Bushy

Answer
Bushy unfortunately you will need a manual. The adjustments are beyond the scope of this web site to answer. The linkages between the carbs are adjusted by the plastic linkage between them and the small machine bolt on the top of the carb.
You should be able to look directly in the front of the carbs to see if they are opening and by the linkage on the top of the carbs.
Make sure your timing is advancing as well.
It sounds like the controls are off as well.
Make sure the two cables are not reversed.
A starter can be retrofitted in some cases, however all of the parts are not all available. You may be better off with another motor with electric start already installed.
Wish I could give you more.
Jeff